Slovakia's Magdalena Rybarikova sent top-seeded Simona Halep crashing out of the WTA Tour's Connecticut Open in one of two second round upsets at the final US Open tune-up.
Halep, the reigning champ, on Tuesday had her serve broken six times and Rybarikova saved 10 of 14 break opportunities en route to a 6-2, 4-6, 6-3 victory at the Connecticut Tennis Center facility.
Second-seeded Petra Kvitova, last year's runner-up to Halep, cruised past Ekaterina Makarova 6-2, 6-1 to reach the quarter-finals in a match that lasted just 48 minutes on the hardcourts.
Unseeded Alison Riske became the first player to reach the quarters by upsetting sixth-seeded Italian Flavia Pennetta, 6-1, 7-6 (7/3).
American Riske, who never trailed in the second set tie-breaker, blasted eight aces and was a perfect five for five on break points in the 94-minute match.
"There are a lot of top players here. I'm definitely proud to be the lone American left, and hopefully I can keep it rolling," she said.
"I knew that I had to attack her second serve because she places her first serve so well. I felt like I was going to get looks at it at any moment, so I just kind of stuck with it, and I ended up returning well today. I just played solid."
Riske jumped out to a 3-1 second set lead, but Pennetta was able to tie it at 3-3. The players held serve the rest of the way, setting the stage for the tie-breaker.
Riske snapped a four-match losing streak with a straight set victory over Casey Dellacqua in her tournament opener. Riske next faces Rybarikova.
In other second round action Tuesday, Czech Barbora Zahlavova Strycova eased past France's Caroline Garcia in straight sets win of 7-5, 6-2.
Zahlavova Strycova had two aces, went four-for-five on break points and saved 12 of 13 on her own serve in the one-hour, four- minute match.